Combustion control



Oct. 28 1924.

G. H. GIBSON COMBUSTION CONTROL Oct. 28, 1924.'

G. H. GIBSON COMBUSTION CONTROL Filed Oct. 19, 1920 4 Sheets-Sheet 2 G. H. GIBSON COMBUSTION CONTROL Oct. 28 1924.

med Qct. 19 1920 -4 sheets-snee: s

Oct. z8. 1924. l 1,513,103

G. H. GIBSON COMBUSTION CONTROL Filed Oct. 19, 1920 4 Sheets-Sheet 4 ATTORNEY Patented Oct. 28, 1924.

UNITED STATES GEORGE H. GIBSON, F MONTCLAIR, NEW JERSEY.'

COMBUSTION CONTROL.

' Application mea octqber 19, 1920. serial No. 418,037.

T o all whom it may concern:

Be it known that I, GEORGE H. GIBSON, citizen of the United States, and resident of Montclair, in the county of Essex and State of New Jersey, have invented certain new and 'useful Improvements in Combusprovide an effective method of and apparatus for automatically regulating the supply of fuel to the fuel bed as required to maintain the fuel bed resistance to gas flow therethrough lapproximately constant.

The invention is especially devised and adapted for use in connection with steam generating boilei furnaces and another specific object of the invention is to provide an improved method of, and apparatus for automatically regulating the rate of combustion in response to the demand on the boiler; and in the practical accomplishment of this object, the supp-ly of the air required for the combustion of fuel is made automatically responsive to the rate at which steam is Withdrawn from the boiler with pro-visions, when desired, for modifying the direct ratio between the rate of steam flow and the combustion and fuel sup-ply rates in response to changes .in the boiler steam pressure.

A preferred form of my invention, as used to regulate combustion in a steam generating boiler furnace comprises cooperating provisions for simultaneously attaining bot of th-e above mentioned specific objects of my invention, but they may be separately attained when conditions make this desir-able.

The -various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, advantages possessed by it, Vand various spe- `citic objects attained with it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described preferred forms of embodiment of the invention.

O f the drawings:

Flg. l is a diagrammatic representation of a stationary boiler furnace plant;

Flg. 2 is yan 'elevation with parts broken and in sections of a portion of the appara tus employed in Fig. 1;

Fig. 3 is an elevation of a portion of the apparatus shown in Fig. 2 taken at right angles to the last mentioned ligure;

Fig. 4 is a sectional elevation of another portion of the apparatus shown in Fig. l;

Fig. 5 is a section on a line 5-5 of Fig. 4; FFigli. 6 is a section taken o-n a line 6 6 of Fig. 7 is a diagram illustrating the elecricallcircuits employed in the apparatus of Fig. 8 is a sectional elevation of a modified form of my invention embodied in a locomotive;

Fig. 9 is fa sectional elevation of a detail of construction employed in Fig. 8; and

Fig. 10 is a diagrammatic representation of another modification of my invention.

In Fig. 1, I have illustrated the use of my invention in connection with a stationary boiler furnace A of conventional type. As shown, the boiler furnace A comprises a fuel bed supporting grate A', with a primary air inlet A2 to the furnace chamber below the grate and with secondary air inlets A3 to the furnace chamber above the grate, and with a products of combustion outlet A* leading to a stack or other draft creating device, the latter being controlled by a stack damper A5. The steam generated in the boiler is Withdrawn through a pipe A8. Fuel is supplied to the grate A by -an automatic Stoker mechanism B10 including 'a vdriving motor B, the speed of which is automatically adjusted as hereinafter exlplained so as to maintain a fuel bed of determined resistance to gas flow therethrough.

Primary air is sup-plied to furnace inlet A2 by a blower or other air moving device driven by a motor C at Ia speed dependent uponthe boiler steam output, and the damper A5 is automatically adjusted as required to maintain a pressure in the boiler chamber 'above theV furnace grate whichoutput of the boiler. This current strengthy 'm the control circuit may vary directly with the rate of steam outow but preferably as shown in Fig. 1, provisions are nrade for modifying the ratio between the rate of steam outflow and the current flow through the control circuit in response to variations in the steam pressure, so that the current iow tends to increase both upon an increase in the rate of steam outflow and upon a decrease in the steam pressure, andtends to decrease upon a decrease in the rate at which steam is withdrawn from the boiler and on an increase in the steam pressure.

The stack damper AE is adjusted by a controller DA comprising an electromagnetic iow balance connected in thecontrol circuit and operating to adjust the damper A5 as required to maintain a predetermined ratio' between the rate of flow of products of com`- bustion through the stack connection A4 and the current in the control circuit. The speed of the Stroker motor B is directly` regulated by a controller DB includin an electromagnetic flow balance connec in the control circuit and adjusting the speed of the motor B in a manner tending to mamtain a predetermined ratio between-the differential of 'the furnace chamberpressures above and below the furnace grate'and the square of the current strength inthe control circuit. The speed of the blower motor C is regulated by a controller DC including m l electromagnetic flow balance connecte the control circuit and adjusting the speed ofthe vmotor C as required to maintain a predetermined ratio between the current in the control circuit and the amount ot rimary air delivered by the blower to the rnace chamber. I

The electromagnetic Lliow balance of the. master controller D see Figs.. 2 and 3, comprises a tilting differential pressure' gauge of the U tube type, the vertical legs D and D2 of which are carried by a frame D3 having a knife-edge pivot DA2 mounted on a bearing D5. Advantageously the legs D may be separately adjusted on arms of the frame member D3 toward and away from the pivot D* ment as by means of the set screws De. The static preure in the steam conduit A is and clamped inany desired adjusttransmitted to the upper end of gauge chamber D. by a iexible pipe F, and the total pressure in the conduit A is transmitted to the upper end of the gauge chamber D2 by a flexible conduit F. The frame D3 comprises Associated with and regulated by the electromagnetic lio-w balance of the master controller D is an electrical current adjusting device or current controller G comprising, in the form shown, a supporting shaft G on which is loosely j ournaled a member G2 having ratchet teeth at its periphery. Also journaled on the shaft Gl is a reciprocating power actuator Jfor current controller G. This actuator comprises a ratchet actuating lever HS. The latter is' oscillated by a constantly running electric motor H through connections including a gear wheel -H5 in mesh with the motor shaft and carrying a crank pin connected by the link H4 to the -lever H3. The latter is provided with two pawls H and H2. The pawl H tends to engage the ratchet teeth onthe periphery ot the member G2 and turn the latter with the lever H3' when the latter swings into the clockwise direction as seen in Fig. 3, while on the return stroke of lever H3, the pawl H2 tends to move the member G2 in the lcounter clockwise direction. A pawl controller D carried by an extension D? of the .o-w balance frame. prevents the simultaneous engagement of both pawls H and' H2 withthe ratchet teeth of the member G2, andregulates the amount and direction of movement imparted to the member G2 bythe movements of the pawls.- As shown the pawl controller is inthe form of an arc shaped strip of sheet metal tting over a portion of the periphery of the member G2 and serving, when the tilting pressure gauge is in its -neutral positionv as shownin Fig. 2, to holdboth pawls H and H2 out of engagement with the ratchet positions of the lever H3. When the tilting pressure gauge is swung from its neutral osition in a clockwise direction as it will be when *the steam'flow through the conduit A increases relative to the current flow through the coils D10, the, shield D9 willy teeth G2 in all hold the pawl H2 out of engagement with the ratchet teeth G2 throughout the complete stroke of the lever H3, but the pawl H will then be permitted to engage the ratchet teeth during a portion. of the movement of vthe lever H2 and correspondingly adjust the member G2 in a clockwise direction as lseen in Fig. 3. The portion of the movement of the lever Hs in which the pawl H operativelyengages'and 4adjusts the member G2 will vary with the extent of displacement of the shield D9 from its neutral position owing to the shaped side edges D2o of the shield member. Similarly when the shield member is displaced to the right from its neutral position as shown in Fig. 2, the pawl H will be held out of engagement with the teeth of the member G2 and the pawl H2 will effect adjustments of member G2 in the counter clockwise direction as seen in Fig. 3 iny steps the magnitude of which depends upon the extend to which the shield D9 is displaced from its neutral position.

The member G includes a resistance G3 wound in a flattened helix about a cylindrical support G50. The terminals of the con# ductor G3 are connected, respectively, to

inner and outer concentrically disposed con-- tact rings G4 and G5. I and J represent stationary brushesengaging the slip rings G5 and G4 respectively and K is a `stationary brush engaging the resistance conductor G3. The brushes I and J (see Fig. 7) are connected by branch conductors 4 and 3, to the main current supply conductors 1 and 2, respectively, between which any suitable potential difference may be maintained.

The coils D10 of the master controller D are connected in a control circuit (see Figs. 1 and 7 including the conductor 4:, brush I,

slip ring G5, the portion of the resistance G5 between the end of the latter connected to the slip ring G5 and the point at which the resistance G5 is engaged by the brush K, the latter, a conductor 15, conductor 16, coils DA1", conductor 17, coils DB1", conductor 1S, coils DC10, conductor 19, and a portion of the conductor 3. The control circuit alsoincludes adjustable resistance shunts R and R hereinafter referred to.

The potential impressed upon this circuit is a fraction of the potential between the supply' conductor 1 and 2 which depends upon the. position of the member G2 relative to the brush K. In the apparatus shown in Fig. 1, a shunt comprising conductors 20 and 21, contact E', and a portion of the resistance R is placed about the windings of the balance coils D10. The contact E is carried by the movable end of a bellows pressure chamber E to the interior of which the static pressure in the steam conduit A6 is transmitted by a pipe E3. With the apparatus shown in Fig. l, the flow balance of the master controller D adjusts the current regulator G as required to maintain an electric current flow through the windings D1o which varies in strength with the rate of steam flow through the' conduit A5. The total current flowing through the control circuit is equal to the sum of the current.

flowing through the coils D1O and the current flowing through the shunt including the conductors 2O and 21. So. long as'the steam pressure remains constant, the current flowing through the coils D10 and the current flowing through the shunt are in the same ratio, and in consequence the total current iiowing through the control circuit varies directly with the current flowing through the coils D10. The tendency of an increase or decrease in the steam pressure in the pipe A5 is to increase or decrease, respectively, the portion of the resistance R in the shunt about the coils D1o and consequently to decrease or increase respectively, the total current flow through the control circuit and to correspondingly decrease or increase the` rate of combustion. In the construction illustrated, the controllers DA, DB and DC each include an electromagnetic flow balance which may be identical with4 the flow balance of the master co-ntroller D. In Fig. 7 DA1", DB10 and D010 indicate the How balance coils of the controllers DA, DB and DC respectively, corresponding to the coils D10 of the balance D. The controllers DA, DB and DG each comprises a motor HA, HB and HC, respectively, corresponding to the motor H of the master controller. The motors HA, HB and HC are connected across the supply lines 1 and 2 by conductors 5, 6; 7, 8; and 9, 10, respectively.

The flow balance of the controller DA controlling the stack damper A5 is made responsive to 'the flow through the stack outlet AI1 by the static and total preure transmitting connections F2 and F3, respectively. The controller DA includes a ratchet lever H3 continuously oscillated` by the motor HA and serving through its pawls H and H2 t0 adjust a gear segment L in response to Athe position of the shield D9 of the controller DA in the same manner in which the position of the member G2 is controlled as above described. The gear segment L is secured to ashaft L on which the ratchet lever H3 is journaled and Ito which is secured a valve member M of the rotary D type valve, the valve M Working in the valve chest O. Interposed between the inner wall of the valve chest and the valve member M is a cylindrical valve mem ber N. The valve chest O is provided with an inlet O for a suitable motive fluid such as water under pressure, with an exhaust outlet O2 and with spaced apart ports connected by pipes O3 and O1 to the opposite ends of the damper actuating cylinder P. Thev piston P working in the cylinder P has its stem P2 connected to the operating arm of the damper A5. The piston stem P2 also is connected by an arm P3, link P1 and arm N3 to the valve member N. The valve member N is formed with spaced apart ports N and N2 the inner ends of which are normally closed by corresponding portions of the valve member M. The

ports in valve member N open at their outer flowing through the coils DA1o rises relative to the fluid flow through the conduitv A4, the shield D9 is shifted to the left as seen in Fig. 5 and the member L is thereby adjusted by the action o-f the p-awl H in the clockwise direction to thereby permit pressure fluid t0 iow from the valve chest O through the pipe O3 into the right hand end of the cylinder P, while at the same time permitting the left hand end of the cylinder to exhaust through the pipe O4 and exhaust outlet O2. This shifts the piston P to the left and opens the damperi A5 thereby increasing the iiow through the conduit A4. An adjustment of the member L in the counter clockwise direction'correspondingly adjusts the damper A5 in the closing direction. With either adjustment of the damper, the corresponding movement of the valve member N produced through the arms l?s and MB and :link P4 tends to prevent over travel and hunting of the piston and damper.

The controller DB for thestoker feed may f be identical in construction with the master controller D except that the resistance conductor G0 of controller DB, as shown clearly in Fig. 7, is not connected to the balance coils DB10 but serves as a means for regulating the speed of the stoker motor B, the shunt field winding B10 of which has one terminal ,connected by the conductor 22 to the brush K of the controller DB. .In the controller DB, the ,brush J and indeed the contact ring G4 are idle elements and may be omitted. As shown the motor B has its terminalsv connected by conductors 13 andl 14, and 11 and 12 to the supply conductors 1 and 2. The second terminal of the shunt field winding B10 of the motor B is connected to the conductor 14. The differential pressurey gauge of the balance DB has its legs connected to the furnace chamber above and below the furnace grate by I the pressure transmitting pipes F5 and F1L respectively. With the described arrangement when the current iiow through the coils DB10v of the controller DB, rises relatively to the differential of the pressures at the opposite sides of the grate A and fuel bed thereby supported`,the current controller G of the balance DB is adjusted in the clockwise direction. This increases the portion of the resistance conductor Cr8 in series with the shunt field winding D10 and thereb reduces the field strength of the motor and increases 'its speed, and thus tends to increase the thickness of the fuel bed and the pressure differential between the opposite sides of the fuel bed. Conversely when the current through the coils DB10 falls relatively to the pressure drop through the fuel bed, the rheostatelement G of, the

controller DB is adjusted inthe counter increases the and reduces clockwise direction and thereb eld strength of the motor the speed of the latter, and thus tends to `produce a reduction in the fuel bed'thickness.

i The controller DC may be identical in construction and arrangement with the controller DB. 23 represents the conductor con-y .of the differential pressure gauge element of the controller DC by a conduit F0 and the total pressure in the blower outlet is transmitted to the other leg of the gauge by a pipe-F7. When the control current flowing through the coils DC10 rises relative to the rate of air flow into the furnace outlet A? the current controller G of the controller -DC is adjusted in a clockwise direction to thus increase the resistance in series with the field .winding C10 and correspondingly increases the speed of the motor C and thereby increase the amount of air supplied to the furnace inlet A2. A decrease' in the strength of current iiow through the coils DC10 relative to therate of air flow into the furnace inlet A2 causesthe rheostat element of the' controller DC to be adjusted in the counter clockwise direction thereby decreasing the speed of the motor C and tileI rate atl which air is passed to the inlet The vmaster controller D tends to maintain a current. flow through the control circuit whichis proportional to the steam iow through the boiler steam pipe A0. The pressure chamber E acting on the resistance R tends to vary the current flow through the control circuit in inverse proportion to the ,changes in steam pressure. The master controller and the pressure chamber E cooperate to` maintain a total current ow through the control circuit which is responsive to the `heat requirements of the boiler furnace. The controllers DA, DB and DC cooperate to maintain a' rate of combustion and a rate of fuel supply proportional to can be independently regulated by manually .yadjusting the corresponding resistance R `to divert more or less of the total current iow in the control circuit through the shunt about the dynamometer coils of the controllcr. The rate of combustion is directl regulated by the controllers DA and D which respectively control the inflow of primary air to the boiler furnace, and the outflow therefrom of products of combustion. These two controlling devices act conjointly to maintain a pressure in the furnace chamber above the fuel bed which varies inversely with the rate of combustion and hence insures the proper influx of secondary air through the inlet A8. The controllers DA and DC can maintain the proper rate of combustion, of course, only in case fuel is kept on the grate A. The controller DB not only insures the continuous maintenance of fuel on the grate A but insures a rate of fuel supply which tends to maintain a fuel bed of approximately constant resistance and thickness as is desirable for eflicient combustion and ease in regulating the rate of combustion.

Variations in the rate of combustion and consequently in the volume of gas flow through the fuel bed do not disturb the tendency of the controller DB to maintain a fuel bed of constant resistance to gas flow through it, since the two opposing forces, acting on the iiow balance, namely, the differential of the pressures transmitted to the gauge element by the pipes F4 and F0, and the electromagnetic action between the stationary and floating coils DB10, both vary in the same proportion and in the same direction with a given change in the volume of draft. The differential between the pressures at the opposite sides of the fuel bed is proportional to the product of the fuel bed resistance multiplied by the square of the volume of flow through the fuel bed. The electro-magnetic force which the stationary coils DB1o exert on the floating coil DB10 is proportional to the square of the current flow through the coils, and this current flow is itself proportional to the total volume of draft. and hence to the volume of gas flow through the fuel bed. The controller DB responds, therefore, to variations in fuel bed resistance and is unaffected by changes in the volume of draft.

While I have said that the controller DB tends to maintain a fuel bed of constant thickness, this is not strictly correct since when the rate of combustionl is relatively rapid, the strong draft necessarily then existing tends to make the fuel bed more open or porous than it is with slower rates of combustion. This increase inporosity or openness of the fuel bed reduces the resistance to gas liow therethrough and in consequence the fuel bed becomes slightly thicker when a rapid rate of combustion is maintained than when the rate of combustion is slower. This thickening of the fuel bed when the rate of combustion is rapid is a desirable feature as those skilled in the art Will readily understand.

The general mode of operation obtained with the apparatus disclosed by way of illustration in Figs. 1 to 7, can be secured with apparatus varying greatly in form therefrom. For example, the very different apparatus shown in Fig. 8, may be employed to maintain a rate of combustion proportional to t-he normal heat requirements of the locomotive furnace shown, and to maintain a fuel bed of constant resistance.

In Fig. 8. AA represents a locomotive of which A10 is the grate,l A12 the firebox, A1* the smoke box, A11 the primary air inlet to the ash pit, A12 the smokestack, A15 the steam dome, A10 the steam pipe leading from the steam dome to the valve chest A11, of the locomotive, and A18 the secondary air inlet. The exhaust pipe A10 leads from the valve chest to an exhaust nozzle Q discharging axially through the smoke stack A12 as is usual. A bellows pressure chamber R has its interior connected by a pipe R to steam pipe A18 and has its mo-vable lower end connected to the stem of a needle valve R2 which throttles the outlet of the exhaust nozzle Q more or less in inverse relation to the locomotive steam pressure. Fuel is fed on to the grate A10 by an automatic stoker mechanism B20'at a rate regulated by the valve B23 controlling the flow of steam through the pipe B22 from the steam dome of the locomotive to the steam motor B21 driving the stoker mechanism.

The extent to which the valve Bz3 is opened and consequently the rate at which fuel is fed on to the grade A10 is controlled by a pressure motor W* and the means provided for regulating the pressure therein. The pressure regulating means comp-rises a pair olf pressure chambers U and U having flexible walls or diaphragme connected to the opposite ends of a lever U2, the fulcrum Ua of which can be adjusted lengthwise of the lever by rotating the adjusting screw U. The pressure chamber U is connected to the lirebox by the pressure tranmnitting pipe U5 and the chamber U is connected to the smoke box by the pressure transmitting pipe Us. The lever U2 carries a needle valve U" which regulates the leakage from a chamber W (see Fig. 9) through an outlet W10. A pipe W3 'connects the chamber W to the pressure motor chamber W2'. A motive fluid tion W which includes a restricted orifice W2. v

With the arrangements described substantially all ofthe steam generated by the locomotive is discharged in normal loperation through the exhaust nozzle Q, and the ejector or draft producing effect of the latter is vtherefore approximately proportionalto the rate of steam output fro-m the locomotive boiler. The effect of the exhaust nozzle is to create a pressure less than that of the atmosphere ini the rebox of the locomotive and a still lower pressure in the -smoke box. The drop in pressure between the rebox and the smokebox is a function on the one hand of the volume of 'low through the boiler tubes and on the other hand of the resistance of the boiler tubes tothe flow through them. Similarly the drop in pressure between the atmosphere and the firebox is al function of the amount of gasflow through the fuel bed and the resistance of the fuel bed to the gas flow through it. If the fuel bed resistance to flow is constant, the difference betweenthe pressure of the atmosphere and the pressure in the smoke box will vary in proportion to the difference between the pressure of the atmosphere and the pressure in the smoke box. Therefore if the fulcrum U8 for the lever U2 is nearer the center of chamber U than to the center of the chamber U when the flexible walls of the two chambers are of the same size, or if the fulcrum is midway between the centers of the two chambers and the diaphragm of the chamber U is smaller than the diaphragm of the chamber U, there will be a certain standard fuel -bed resistance to flow which will maintain the lever U in euilibrium regardless o f whether the rate `through the inlet A18.

When the` fuel bed resistance to flow becomes greater than the predetermined standard, the differential between the pressure of the atmosphere'and that in the. rebox increases ative to the differential between the pr re of the atmosphere and that in the smo e box, and this shifts the lever U2 in the direction moving the needle valve U" farther into the vorifice W0 and thereby causesl thewpressure in the pipe W8 and the chamber- 4 izo-build up. This moves the valve B2a inthe closing direction, throttles the supply'of steam to the stoker motor B21, reduces the rate of fuel supply to the grate and thereby brings about a reduction in fuel bed thickness and resistance. Conversely when the fuel bed resistance falls below the standard value, the lever U2 is shifted to withdraw the needle valve U7 somewhat,

whereby the pressure in the' pipe W3 -and chamber W4 is reduced, and the valve B23 is correspondingly opened by the springI B24, thus speeding up the stoker mo-tor and\ the valve R2 and located in the live steamsupply connection -S to the live steam aux# iliary draft creating nozzle S is opened, thus increasing the dra t and tending to bring the steam pressure up to normal. The auto- *l* matic control of the draft effected by the discharge through the exhaust nozzle Q, and the pressure chamber R may be supplemented, if desired, by the auxiliary steam supply throughV the pipe X and manuauy. controlled Valve X to the live steam draft nozzle S.v

It is to be noted that the maintenance of a const-ant relation between the' drop in draft pressure between points immediately above and below thefuel bed and the drop in `draft pressure through the subsequent portion of the furnace system in which the 'low resistance is constant which is obtained directly with the apparatus of Fig. 8 is obtained indirectly with the apparatus of Fig. 1. With the apparatus of Fig. l this result is obtained indirectly since the volume of draft land the pressure drop through the fuel bed are both kept proportional to the same qu-antity. 'Ihe same result is also directly obtained in the modified construction shown in Fig. 10 wherein the furnace system shown by way of illustration is identical with that of Fig. 1, except that the secondary air is supplied from the ashl pit of the furnace through a by pass A2, of regustack'connection A4.v For thispurpose one end of the lever U2 is subjected to the opposing action of the flexible diaphragm walls of a pair of pressure chambers U and U21, one connected to the furnace ash pit and the other to the furnace chamber immediately above the fuel bed; while the other end of the lever is subjected to the opposing action of the flexible walls of a pair of pressure chambers U22 and U22 connected one to the furnace chamber immediately above the fuel bed and the other to the smoke stack connection A4.

It will be apparent to those skilled in the art without further explanation that the same sort of control of the supply of fuel bed is had with the apparatusof Fig. 10 as with the apparatus of Fig. 8. The pressure chambers U21 and U23 in Fig. 10 are necessary to compensate for variations in stack suction. If the pressure in the stack connection A4 were always atmospheric, the

two chambers U21 and U23 of Fig. 10 would be unnecessary and might be dispensed with in which case the fulcrum U for the lever U2 should be adjusted toward the chamber U20.

The regulation of the supply of fuel to the fuel bed so as to maintain a constant fuel bed resistance to gas flow therethrough is desirable, regardless of how the volume of draft and combustion rate. are controlled. It could be had advantageously for example with the apparatus shown in Fig. l() if the control of the stack damper A5 and the blower motor C thereof were purely manual,

or if the blower C and stack damper A5 were controlled in automatic response to the steam output from a battery of boilers of which the boiler shown in Fig. 10 is one unit, or were controlled as in other known systems of combustion regulation. Novel features of the fuel feed control employed in the construction shown in Fig. 8 hereof but not claimed herein are claimed in my copending application, Serial No. 583,491 filed August 22, 1922.

While in accordance with the provisions of the 'statutes I have illustrated and described the best forms of my invention now known to me, it will beapparent to those skilled in the art that many changes may be made in the forms of the apparatus and modes of operation described without departing from the spirit of my invention as set forth in the appended claims.

Having now described my invention, what lI claim as new and desire to secure by Letters Patent, is:

1. The combination with .a furnace having a furnace chamber and a fuel bed supporting grate in the furnace chamber and normally open primary and secondary air inlets opening to the furnace chamber at opposite sides of the grate, of means regulating the total volume of draft through the 2. T hc combination in a furnace having a furnace chamber a burning fuel bed the-rein, and an inlet thereto for primary air, and an inlet thereto for secondary air, of means jointly responsive to the volume of draft and to the resistance of the fuel bed to flow therethrough for maintaining a predetermined ratio between the resistance to iiow through the fuel bed and the resistance to iow through said secondary air inlet.

3.,Control apparatus comprising in combination a tilting differential pressure gauge element, a Winding carried by Athe tilting gauge element, a cooperative stationary winding and means for creating an electric current flow through said windings exerting an electromagnetic action on the rst mentioned winding tending to hold the gauge element in a neutral position, comprising an adjustable current controller, a reciprocating-actuator for said current controller, and means moved by the gauge element controlling a. mechanical connection between said actuator and current controller whereby the actuator is prevented from operating said controller or is made effective to operate the latter in one direction or the other accordingly as said gauge is in a neutral position or is displaced therefrom in one direction or the other.

4. In control apparatus the combination with an instrument element displaceable in opposite directions from a neutral position, of a relay mechanism comprising a member mounted for reciprocatory miofvement, a reciprocating actuator, a clutch mechanism carried by said actuator and adapted to connect said actuator and member for movement together, means moved by said instrument element and moved by the latter in a direction transverse to the plane of movement of said member adapted to render said clutch mechanism inoperative to connect said actuator and member for movement in either direction in the neutral position of said instrument element, and adapted to render said clutch mechanism inoperative. to connect the actuator and member for movement in one direction or the other when said element is displaced from the neutral position according to the direction ofthe displacement. f

5. In control apparatus the combination with an instrument element displaceable in opposite direction from a neutral position, of a rela-y mechanism comprising a pivotally mounted member provided with ratchet teeth, a pivotally mounted actuator, means for oscillating said actuation, a pair of pavvls carried by said actuator, one adapted to couple the actuator and member for movement togethe-r in one direction and the other vadapted to connect the actuator and member for movement in the opposite direction, and a pavvl controller moved by the instrument element in a direction transverse to the piane of rotation of said member and adapted to render both or one or the other of said paWls inoperative accordingly as the instrument element is in a neutral position or is displaced therefrom in one direction or the other.

6. In control apparatus the combination with aninstrument element displaceable in opposite directions from a neutral position, of a relay mechanism comprising a pivotally mounted member provided With ratchet teeth, a pivotally mounted actuator, means for oscillating it, a pair of pawls carried by said actuator, one adapted. to couple the actuator and member for movement together in one direction and` the other adapted to couple the actuator and member for movement in the opposite direction,

` and a pawl controller moved by the gauge element in a direction transverse to the plane of rotation of said member and lating the operativeness of the pawl not totally inoperative in accordance with the degree of displacement.

7. In a iiow balance the combination with a tilting differential pressure gauge and electromagnetic means adapted to hold said gauge in a neutral position When energized by an electric current of proper strength, of means for adjusting the strength of said energizing current comprising a current controllera power actuator, and means moved by said gauge when displaced in either direction from a neutral position for mechanically coupling said actuator to said current controller to actuate the latter in the direc- 4tion tending to vary the energizing current as required 'to restore said balance to its neutral position. p

8. In a boiler furnace system in which solid fuel is burned in a bed on a grate, Withe and the .ow of gases from the furnace in response to the boiler load, a mechanical Stoker, and automatic controlling means therefor jointly responsive to the dra-ft loss through the fuel bed and tothe boiler load. Signed at New York in the county of New York and State of New York this fourteenth day of October A. D. 1920.'

GEORGE H. GIBSON. 

